The invention relates to a central release device for a hydraulic clutch actuation system. The invention relates in particular to a central release device of a hydraulic clutch actuation system for a motor vehicle clutch.
A conventional hydraulic clutch actuation system for motor vehicles has a master cylinder which is connected to a compensating reservoir filled with hydraulic fluid and which can be actuated via a clutch pedal. The master cylinder is hydraulically connected via a pressure line to a slave cylinder, so that the pressure produced in the master cylinder by depressing the clutch pedal can be transmitted to the slave cylinder via the fluid column in the pressure line. The release bearing of the clutch is as a result subjected by the slave cylinder to an actuating force in order to separate the clutch pressure plate from the clutch driving disc and thus the engine from the transmission of the motor vehicle.
In order to guarantee smooth clutch actuation with a small space requirement for the slave cylinder, the prior art has proposed forming the slave cylinder as an annular cylinder which is disposed around the clutch or transmission shaft and attached to the transmission. An annular piston is disposed in sliding fashion in the axial direction of the clutch or gear shaft in the annular cylinder and is connected for operation to the release bearing of the clutch. When the annular cylinder is acted upon hydraulically via the pressure line, the annular piston acts via the release bearing on the release lever of the clutch in order to release the latter. Because they are disposed concentrically with the clutch or transmission shaft, slave cylinders of this kind are also called central release devices.
The prior art is not lacking in proposals as to how such central release devices should be formed (e.g. EP 0 095 841 B1, EP 0 168 932 B1, DE 41 09 125 A1, DE 43 13 346 A1, DE 197 42 468 A1). A feature common to the central release devices considered here is the fact that they have a housing which comprises a through-bore, is cut out of a metallic material or injection moulded from a plastics material and can be attached to a transmission wall in the motor vehicle. A drawn steel sleeve is provided coaxially with the housing in the bore, this sleeve comprising at the end a flange which extends in the radial direction and is disposed between the housing and the transmission wall when the central release device is in the mounted state. In this prior art the inner circumferential face of the bore defines, together with the radial flange and the outer circumferential face of the steel sleeve, the pressure chamber containing the annular piston which is guided on the steel sleeve and provided with a sealing element.
In order to seal off the pressure chamber, an elastomeric sealing ring is generally provided between the housing and the flange of the steel sleeve. The steel sleeve is also connected in a fixed fashion at its flange to the housing by means of a screwed connection (EP 0 095 841 B1), by caulking the housing (EP 0 168 932 B1), by means of a retaining ring (DE 41 09 125 A1), by a welded joint, riveting, through-fitting or a rolling connection (DE 43 13 346 A1) or by means of a snap connection (DE 197 42 468 A1), so that the sealing ring between the housing and the flange of the steel sleeve and the sealing element at the annular piston are not accessible and therefore cannot be damaged. However this prior art has the disadvantage of entailing a high expenditure to form the connection between the housing and the flange of the steel sleeve, and this constitutes a significant proportion of the production costs of this mass-produced article.
As compared with the prior art according to EP 0 168 932 B1, which constitutes the type in question, the object of the invention is therefore to provide a simply formed central release device which can be produced more conveniently without the risk of functional problems.
This object is solved by central release device for a hydraulic clutch actuation system, with a housing and a sleeve provided with a flange, which together define a pressure chamber for accommodating an annular piston, by means of which a release bearing guided on the sleeve can be displaced, wherein a spring, which braces the housing and the release bearing apart, subjects the housing to a force directed at the flange, and a seal is provided between the housing and the flange to seal off the pressure chamber, wherein there is a retaining element, which can be detached to operate the central release device and which, when the central release device is in the non-mounted state, forms a stop for the housing and prevents the housing alone from moving against the force of the spring away from the flange of the sleeve beyond a predetermined amount.
According to the invention, given a central release device for a hydraulic clutch actuation system which comprises a housing and a sleeve provided with a flange, which together define a pressure chamber for accommodating an annular piston, by means of which a release bearing guided on the sleeve can be displaced, wherein a spring, which braces the housing and the release bearing apart, subjects the housing to a force directed at the flange, and a seal is disposed between the housing and the flange to seal off the pressure chamber, a retaining element, which can be detached to operate the central release device, is provided which, when the central release device is in the non-mounted state, forms a stop for the housing and prevents the housing alone from moving against the force of the spring away from the flange of the sleeve beyond a predetermined amount.
In other words, there is no fixed connection between the housing of the central release device and the sleeve, so that the production of the central release device is simplified overall. In this respect the invention utilises the knowledge that the systems known from the prior art for attaching the sleeve to the housing are only actually required until the central release device is mounted in the housing, as when the central release device is in the mounted state the flange of the sleeve is secured on one side between the housing of the central release device and on the other side a housing wall or a housing cover of the transmission, to which the housing of the central release device is attached, e.g. by means of screws. The detachable retaining element is provided according to the invention for the purpose of packing, storing, transporting and mounting the central release device, which element, being assisted by the claimed securement of the housing in relation to the flange of the sleeve, preventsxe2x80x94via the spring already provided in the prior art for reasons relating to function and noisexe2x80x94the seal between the housing and the flange of the steel sleeve or the sealing element at the annular piston from being accessible and in this connection damaged, which could result in leakages during operation of the central release device. The retaining element, which is to be detached to operate the central release device after it has been mounted in the motor vehicle, can advantageously be reused or is repeatedly reusable. A further advantage lies in the fact that the seal between the housing and the flange of the sleeve can easily be replaced should this appear necessary on account of material ageing, for example.
Preferably, the housing is expediently provided at its end face which is turned towards the flange of the sleeve or the flange of the sleeve is provided at its end face which is turned towards the housing with an annular groove which accommodates the seal, the thickness of which is greater in the non-deformed state than the depth of the annular groove, wherein the predetermined amount by which the housing can move away from the flange of the sleeve when the central release device is in the non-mounted state is less than or equal to the depth of the annular groove. Therefore, when the central release device is handled outside of the vehicle as mentioned, the retaining element reliably prevents the seal from sliding out of its predetermined position and being damaged between the end face of the housing and the end face, lying opposite this, at the flange of the sleeve.
There are various preferred arrangement variants for the retaining element, in which the release bearing is in each case guided on the sleeve by a sliding sleeve, which is held at the sleeve by means of a stop, and the retaining element is formed as a cross slide. According to claim 3, this cross slide can advantageously be secured positively and non-positively at the sleeve in an annular gap between the sliding sleeve and the housing. The cross slide may alternatively be secured positively and non-positively at the sliding sleeve in a groove made in the outer circumference of the sliding sleeve or at an offset made at the outer circumference of the sliding sleeve. This arrangement variant relates to central release devices in which the sliding sleeve always, i.e. even in the completely withdrawn state when lying against the stop of the sleeve, engages in the annular gap between the housing and the sleeve with its end which is turned towards the flange of the sleeve (see, e.g. EP 0 168 932 B1). According to a further alternative, the cross slide may be secured positively and non-positively at the housing in a groove made in the outer circumference of the housing or at an offset made at the outer circumference of the housing and comprises a stop face for a protective sleeve which is attached to the sliding sleeve and surrounds the housing telescopically, as known, for example, from EP 0 095 841 B1, or for an abutment, attached to the sliding sleeve, for the spring.
Preferably, the cross slide expediently comprises a handle part from which two arms extend which, viewed in a plan view, essentially form a C shape. In order to improve handling of the cross slide, the handle faces of the handle part may each be provided with a profile.
The arms of the cross slide can spring out elastically and comprise a part-cylindrical inner circumferential face, wherein the clearance between the arm ends is slightly smaller than the diameter of the part-cylindrical inner circumferential face, so that, depending on the arrangement variant, the cross slide engages behind the sleeve, the sliding sleeve or the housing like a snap connection in the mounted state. As a result, the cross slide is advantageously prevented, in a simple manner, from unintentionally separating from the central release device.
Preferably, the arm ends are provided at the sides which are turned towards one another with a respective fitting bevel, which makes it easier to fit the cross slide to the central release device.
The securing element or cross slide can be produced particularly easily and inexpensively if it consists of a plastics material. Finally, preferably, the housing of the central release device advantageously consists of a plastics material, while the sleeve is made of steel.